The invention relates to a process for producing a jacketed fuse which must withstand high temperatures and pressures, wherein an unfinished core of explosive material is surrounded by a jacket of a synthetic resin which is shrinkable and to the fuse product.
German Utility Model 7,003,114 discloses a fuse resistant against increased temperatures and pressures. Such fuses are required, for example, for seismic measurements of geological formations wherein the depth of the borehole can amount to more than 4,000 meters, with rock temperatures of between 130.degree. and 200.degree. C. and pressures of up to 1,500 bar. The conventional fuse consists of an unfinished cord, made up of a wrapped and/or a braid-encased explosive core, and a sealing jacket. Film strips of a temperature- and pressure-resistant material are utilized for the sealing jacket. The sealing jacket is covered, in turn, with still further braided threads. Wrapping of the unfinished cord with film strips is a complicated and expensive procedure and harbors the danger of leakages. Therefore, in addition to the sealing jacket, an external jacket is additionally needed and is made up of a solution applied by a dipping method. Such an external jacket, however, due to its minor layer thickness and on account of nonuniform layer thicknesses, can only provide a limited protective function.
It is furthermore known to provide an unfinished cord which contains an explosive with a jacketing produced by hot extrusion of a synthetic resin, for example polyethylene. The synthetic resins suitable for hot extrusion require high extrusion tempertures of about 200.degree. C. Since the unfinished cord contains an explosive, according to the nature of the explosive used in a particular case, a considerable safety risk is incurred during encasing of this unfinished cord with a hot plastic, because there is the danger that the explosive will be ignited. In order to conteract this danger, the jacketing is applied by a cold extrusion method, using cold-extrusible synthetic resins which are subsequently hardened by drying. The preparation of the raw material extrudable composition necessary for this purpose takes at least three weeks, and at least six additional weeks are needed for curing the jacket. This extraordinarily prolonged manufacturing process is accompanied by considerable costs and large expenditure for storage.